class_docstr: This class defines a set of transition which is applied to a configuration to get another configuration
  Note that for different parsing algorithm, the transition is different.
docstr: Note that the algorithm for left-arc is quite similar except for precondition for both arc-standard and arc-eager
  
  :param configuration: is the current configuration
  :return: A new configuration or -1 if the pre-condition is not satisfied
docstr_tok: ["Note","that","the","algorithm","for","left-arc","is","quite","similar","except","for","precondition","for","both","arc-standard","and","arc-eager",":","param","configuration",":","is","the","current","configuration",":","return",":","A","new","configuration","or","-1","if","the","pre-condition","is","not","satisfied"]
code: def left_arc(self, conf, relation):
      """
      Note that the algorithm for left-arc is quite similar except for precondition for both arc-standard and arc-eager
  
      :param configuration: is the current configuration
      :return: A new configuration or -1 if the pre-condition is not satisfied
      """
      if (len(conf.buffer) <= 0) or (len(conf.stack) <= 0):
          return -1
      if conf.buffer[0] == 0:
          # here is the Root element
          return -1
  
      idx_wi = conf.stack[len(conf.stack) - 1]
  
      flag = True
      if self._algo == TransitionParser.ARC_EAGER:
          for idx_parent, r, idx_child in conf.arcs:
              if idx_child == idx_wi:
                  flag = False
  
      if flag:
          conf.stack.pop()
          idx_wj = conf.buffer[0]
          conf.arcs.append((idx_wj, relation, idx_wi))
      else:
          return -1
  
imports: import pickle
  import tempfile
  from copy import deepcopy
  from operator import itemgetter
  from os import remove
  from nltk.parse import DependencyEvaluator, DependencyGraph, ParserI
label_desc: Use image node_id 2 for calling the Transition obj's underlying member method code with example usage: obj.left_arc(conf, relation) and returns: unknown, unknown, unknown